Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 290352
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
852 PM PDT SUN AUG 28 2016

.DISCUSSION...Coastal low clouds did not quite clear and will
remain in place overnight. High temperatures today were about the
same as yesterday but there is a stronger westerly winds aloft and
this showed up a slightly stronger afternoon winds; although,
favored areas such as the Shasta Valley was quite gusting up to 30
mph for a few hours. The new model run is consistent with stronger
southwest winds Monday afternoon as a stronger 700mb winds mix to
the ground, especially in the Shasta Valley and east of the
Cascades. Current forecast covers this trend and no update to the
grids will be issued this evening.

&&

.AVIATION...29/00Z TAF cycle...Along the coast and over the coastal
waters...widespread IFR cigs will persist through Monday morning.
There is some uncertainty whether the coastal ceilings will lower to
IFR. The current TAF reflects coastal conditions lowering to IFR
based on persistence and the consensus of guidance. Given that
onshore flow persists and likely strengthens tomorrow, expect clouds
to impact the coast for most of the day.  Clouds may make it to KRBG
briefly Monday morning but should clear quickly.  Lastly, smoke and
haze will impact airspace with lower visibilities near the Gap Fire
in northern Siskiyou County through tomorrow, spreading north into
Jackson County at least. SK


&&

.MARINE...Updated 200 PM PDT Sunday 28 August 2016...Winds and
seas will be light through tonight. Northwest swell 2-3 feet at 8
seconds will continue through Tuesday. South winds will increase
well ahead of a front Monday afternoon, but they will remain below
small craft advisory criteria. That front will move through the
waters Tuesday night. More fronts will follow Wednesday through
Friday, but none of them are expected to bring small craft
conditions. In fact we may not have small craft conditions until
next Saturday at the earliest. MP/SK


&&

.PREV DISCUSSION... /Issued 500 PM PDT SUN AUG 28 2016/

Updated aviation discussion.

DISCUSSION...The extent of overcast along the coast due to
stratus has diminished. Skies are sunny inland though with
increasingly hazy/smoky skies in Siskiyou and Jackson Counties...
largely due to the Gap wildfire near Seiad Valley in northwest
Siskiyou County. The mid-level steering flow will veer to
northwest and weaken tonight, but southerly flow will return late
tonight and continue through Monday morning before winds veer to
westerly again Monday afternoon.

As mentioned in the previous couple of discussions, the model
trend has been toward weaker cooling (though it will still become
noticeably cooler with temperatures slightly below normal), less
of an increase in humidity, and a lower probability of rain with a
series of systems to brush past our area to the north this week.
But, there is one potentially notable exception on Tuesday. The
main adjustments to the forecast were to adjust the probability of
precipitation to fit a blend of the latest model data. This
included expanding the coverage in area and time of a slight
chance of shortwave induced thunderstorms from Tuesday morning
into early Tuesday evening. The shortwave is now far offshore from
southern California, near 30N 135W. It is expected to weaken
slightly before reaching our area and will contain a relatively
meager amount of moisture as it tracks northeastward. It is
expected to be a fast mover and reach western Siskiyou County
Tuesday morning then track over the southern Oregon Cascades
toward Crater Lake and northern Klamath County during Tuesday
afternoon. The fast movement and low moisture levels will limit
thunderstorm activity to isolated at the most, but it also means
that any lightning will be accompanied by very little, if any,
rainfall.

First, the marine layer will expand into the coastal valleys again
tonight. As another hint at the change in our weather, the stratus
is expected to reach farther inland...to Roseburg in the early
morning hours. Patchy drizzle is likely to accompany the deeper
marine layer. The low clouds will retreat back to the coast during
Monday before a stronger/deeper marine push Monday night. Inland,
it will be sunny on Monday though it will be a few degrees cooler
than today. Also, westerly winds will be stronger...strongest east
of the Cascades with a focus from the Klamath Basin northeastward
into Lake County.

The aforementioned southern stream trough will get caught up in large
scale trough deepening over the eastern Pacific. The main low is
in the Gulf of Alaska and will move quite slowly southeast toward
the Pacific Northwest. After the shortwave passes on Tuesday, a
cold front is expected to reach the coast late Tuesday night then
move across the west side through Wednesday. Rainfall from this
system will be light and likely only at the Oregon coast into
Douglas County and northward. It is likely to be well to the north
..from around Portland northward that a wetting rain would be
possible.

Another front will accompany the large scale upper level trough
axis as it finally swings inland late Thursday afternoon into
early Friday. This front will likely be stronger and produce more
rainfall...but once again the bulk of it is expected north of our
area.

A weaker wave is likely to follow on Friday with the flow aloft
becoming due westerly for a decrease in clouds and slight warming. Model
agreement rapidly diminishes for the holiday weekend, though the
pattern looks to remain active with onshore flow and temperatures
remaining a few to several degrees below normal.

AVIATION...29/00Z TAF cycle...Along the coast and over the coastal
waters...widespread MVFR/IFR cigs will persist through Monday
morning. There is some uncertainty whether the coastal ceilings that
are currently MVFR will lower to IFR. The current TAF reflects
coastal conditions lowering to IFR based on persistence and the
consensus of guidance. Given that onshore flow persists and likely
strengthens tomorrow, expect clouds to impact the coast for most of
the day. Clouds may make it to KRBG briefly Monday morning but
should clear quickly. Lastly, smoke and haze will impact airspace
with lower visibilities near the Gap Fire in northern Siskiyou
County through tomorrow, spreading north into Jackson County at
least. SK

MARINE...Updated 200 PM PDT Sunday 28 August 2016...Winds and
seas will be light through tonight. Northwest swell 2-3 feet at 8
seconds will continue through Tuesday. South winds will increase
well ahead of a front Monday afternoon, but they will remain below
small craft advisory criteria. That front will move through the
waters Tuesday night. More fronts will follow Wednesday through
Friday, but none of them are expected to bring small craft
conditions. In fact we may not have small craft conditions until
next Saturday at the earliest. MP/SK

FIRE WEATHER...Updated 300 PM PDT Sunday 27 August 2016...Dry and
hot weather will continue into Monday. Low clouds and fog will
persist near the coast. Winds will be gusty east of the Cascades
Monday afternoon. This combined with low relative humidities will
make for Red Flag conditions over part of that area...and a Red
Flag Warning is now in effect. A disturbance will move up from the
southwest Tuesday and this will bring a slight chance of
thunderstorms to northern California and Oregon from the Cascades
east. The first in a series of cold fronts will move onshore
Tuesday night...and Wednesday through Friday will be cooler with
occasional showers. -JRS

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from noon to 9 PM PDT Monday for ORZ624-625.

CA...Red Flag Warning from noon to 9 PM PDT Monday for CAZ285.

Pacific Coastal Waters...None.

$$

FJB/JRS/NSK



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